Colored inks can be bought at any artists’ supplier and they have the dual quality of being used with a pen or a brush.
When used with a brush and diluted with distilled water they behave almost exactly like watercolor except that they are far more brilliant in hue. Used with white ink they have all the sparkle of oil, especially if you glaze, using transparent washes of ink over solid white underpainting, as you do when painting with oil. They are easily transported and make a good addition to your outdoor drawing kit.
A mixture of yellow and blue will make an olive green. The red and blue will make a form of purple or violet. Should you particularly want a good purple or violet I would suggest the addition of a purple lake or alizarin crimson. The alizarin will make a good purple with the monastral blue.
You won’t have too much difficulty in mixing watercolors on the palette. They readily fuse with the water. The snag comes when you apply them to the paper with washes.
HOW TO APPLY A WASH
Mix up some blue with plenty of water. Take your large brush for this. Then, on a piece of stretched paper, slightly dampened, put a broad brushstroke across it and observe what happens. Underneath do the same with some red, only this time, after it has started spreading, try to curtail the spread with a clean dry brush. Keep your board tilted while doing this, watch the color spread and find its own level.
You won’t be able to control the behaviour of watercolor very much, consequently it is better to know what the colors do when you apply them and so allow for their caprices. And watercolor is very capricious. It won’t let you overpaint very much. Try doing so over those first washes when they are dry, by placing further washes in the same way. The more you overpaint, the duller the colors become.
Next try gradating a wash by tilting the board after you have placed a full brush of color at the top of your paper, letting it slowly spread downwards, then, by taking a clean, dry brush, try gradating the wash. It is not easy to do so.
Watercolor easily becomes streaky and patchy. To get over this nuisance, J. M. W. Turner, the great English painter, who lived during the last century, used to dip his paintings into barrels of clean water to wash them out a bit. Then, when they were nearly dry, he would start on them again. He is reported as saying that the best brush in watercolor painting was the tap. He had a point there.
The Victoria and Albert Museum has a vast collection of pure watercolor paintings by Constable, Cox, De Wint, etc. who all painted in the pure, transparent way. If you like pure watercolor you will be able to see all the best examples of the way in which different people have used this medium here.